Bug 820237

+++ This bug was initially created as a clone of Bug #820116 +++

Description of problem:
If there is PV with zero PE count in the VG, vgcfgrestore on the VG fails saying "Floating point exception", which is caused by division by zero.

Background:
We are using LVM heavily for storage of block device backups. Because the PVs are usually very busy and metadata manipulation requires direct access to the metadata sector (may take considerable time to complete), we have created a metadata-only PV on a separate drive. 

Version-Release number of selected component (if applicable):
  LVM version:     2.02.87(2)-RHEL6 (2011-10-12)
  Library version: 1.02.66-RHEL6 (2011-10-12)
  Driver version:  4.22.6

How reproducible:
Always

Steps to Reproduce:
create /dev/<metadata_device> with size 200M
create /dev/<data_device> of any size
pvcreate --metadatasize 128m /dev/<metadata_device>
pvcreate --metadatasize 128m /dev/<data_device>
vgcreate -s 128m myVG /dev/<metadata_device> /dev/<data_device>
vgcfgbackup myVG
vgcfgrestore myVG
  
Actual results:
Last command fails with "Floating point exception" error. 

Expected results:
vgcfgrestore should successfully write VG metadata

Additional info:
This issue may be worked around by omitting the zero-length PV from the backup file. See file contents below.
We have solved this for our case using the above workaround and making the metadata PV bigger and setting allocable to N afterwards.

Backup file contents:
# Generated by LVM2 version 2.02.87(2)-RHEL6 (2011-10-12): Wed May  9 10:13:28 2012

contents = "Text Format Volume Group"
version = 1

description = "vgcfgbackup -f myvg.vg myvg"

creation_host = "localhost.localdomain"	# Linux localhost.localdomain 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6 19:48:22 GMT 2011 x86_64
creation_time = 1336551208	# Wed May  9 10:13:28 2012

myvg {
	id = "ouGQeP-8bPl-udT8-lm8a-Nd3A-WprB-pOGXfj"
	seqno = 1
	status = ["RESIZEABLE", "READ", "WRITE"]
	flags = []
	extent_size = 262144		# 128 Megabytes
	max_lv = 0
	max_pv = 0
	metadata_copies = 0

	physical_volumes {

		pv0 {
			id = "hbMvQA-zTeD-CKPc-WE8o-umlm-Z6GJ-iyALRr"
			device = "/dev/vg_test/pv1"	# Hint only

			status = ["ALLOCATABLE"]
			flags = []
			dev_size = 20971520	# 10 Gigabytes
			pe_start = 264192
			pe_count = 78	# 9.75 Gigabytes
		}

		pv1 {
			id = "K1BwfU-2LuG-8aeW-IXHR-RLf7-d36V-DMERDr"
			device = "/dev/vg_test/pv_metadata"	# Hint only

			status = ["ALLOCATABLE"]
			flags = []
			dev_size = 409600	# 200 Megabytes
			pe_start = 264192
			pe_count = 0	# 0 Kilobytes
		}
	}

}


Backup file for workaround:
# Generated by LVM2 version 2.02.87(2)-RHEL6 (2011-10-12): Wed May  9 10:13:28 2012

contents = "Text Format Volume Group"
version = 1

description = "vgcfgbackup -f myvg.vg myvg"

creation_host = "localhost.localdomain"	# Linux localhost.localdomain 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6 19:48:22 GMT 2011 x86_64
creation_time = 1336551208	# Wed May  9 10:13:28 2012

myvg {
	id = "ouGQeP-8bPl-udT8-lm8a-Nd3A-WprB-pOGXfj"
	seqno = 1
	status = ["RESIZEABLE", "READ", "WRITE"]
	flags = []
	extent_size = 262144		# 128 Megabytes
	max_lv = 0
	max_pv = 0
	metadata_copies = 0

	physical_volumes {

		pv0 {
			id = "hbMvQA-zTeD-CKPc-WE8o-umlm-Z6GJ-iyALRr"
			device = "/dev/vg_test/pv1"	# Hint only

			status = ["ALLOCATABLE"]
			flags = []
			dev_size = 20971520	# 10 Gigabytes
			pe_start = 264192
			pe_count = 78	# 9.75 Gigabytes
		}
	}

}

--- Additional comment from agk on 2012-05-09 08:51:02 EDT ---

Thanks for reporting this!

Peter has committed a fix for the next upstream release (2.02.96) and this will be picked up by RHEL6.4:

http://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=501a2c04a4cb009a4c6497cd601801b2fe32fb4e